The objective of the proposed research is the assignment of gene loci to chromosome regions using gene-chromosome linkage analysis in interspecific somatic cell hybrids. Through observation of concordant segregation of human genes and human chromosomes from iinterspecific cell hybrids, twenty human gene loci have been assigned to 14 different autosomes in recent months, indicating rapid porgress in this area of research. By hybridizing cells from individuals carrying balanced translocations or deletions we plan to assign gene loci which are constitutively expressed in hybrid cells and which are known to be on a rearranged chromosome to chromosomal subregions. With new cytogenetic techniques we are able to distinguish more than 300 defined regions within the human haploid genome. The twenty different reciprocal transsocations and deletions available for cell fusion experiments have been studied with banding techniques by the principal investigator; the points of chromosome breakage and rejoining have been established. Hybridization experiments with several rearrangements involving the same chromosome but with different breakpoints will provide insight in the distribution and linear order of genes on chromosomes.